The present invention relates to a process for measuring the permeability to gas of the walls and/or the closure of threedimensional encasing elements, such as heat-sealed packages, bottles or cans, in accordance with a manometric measuring method.
Under the manometric measuring method for determining the permeability of an encasing element for gas, vacuum is produced on the outer side of the test piece. In accordance with the permeability of the encasing element a certain amount of gas passes through the wall per unit of time and brings about an increase in pressure. The permeability to gas can be calculated from the increase in pressure per unit of time.
In regard to the testing of sheets, standards are available for the calculation, e.g., in accordance with the DIN No. 53380. According to this standard, the permeability to gas is expressed in cm.sup.3 of diffused amount of gas per 24 hours and per m.sup.2 of sheet surface. The amount of gas is converted in this connection to the volume at 0.degree. C and 760 torr.
The measuring method worked out for sheets can logically be transferred to closed encasing elements. However, the degree of permeability determined in this connection can be expressed only as an amount per test piece.
Of course, this process which is already novel as such could be realized only on encasing elements that are able to bear a pressure difference of one atmosphere, such as relatively thick-walled bottles. On the other hand, the manometric measuring method cannot be readily applied to thin-walled or semirigid encasing elements, such as bottles of synthetic resin or soft foil packs, since the encasing element is inflated or bursts apart during the measurement.